Titanium braze foil

ABSTRACT

The present invention provides a braze foil comprising titanium and zirconium layers covered by one or more layers of copper, nickel or an alloy of copper and nickel such that neither the zirconium or titanium layers are exposed to the atmosphere. The braze foil may further be layered onto a base material during production to form a braze-clad base material. Methods for brazing a base material with the braze foil are also provided.

BACKGROUND OF THE INVENTION

The present invention relates generally to titanium braze foils and moreparticularly to titanium braze foils with zirconium.

Braze alloys based on titanium (Ti) are useful for braze components thatconsist of titanium, nickel (Ni) and/or iron/steel (Fe) based elementsor alloys, among other uses. Thin gauge braze sheets or foils haveproven useful for preplacing filler metal in braze joints and/or forbonding to base metal materials to form a clad base-metal structure thathas its own braze filler on the surface. The lower melting points ofcommon Ti-based braze alloys cause a beneficial minimum effect on themicrostructures and mechanical properties of the brazed components.Furthermore, Ti-based braze alloys tend to provide corrosion resistancethat is superior to conventional copper (Cu) or silver (Ag) based brazealloys.

Ti alloys undergo microstructural changes when they are processed abovetheir beta transus. The beta transus of Ti alloys refers to thetemperature at which Ti undergoes a complete phase transformation froman alpha plus beta microstructure to an all beta structure or vice versaand results in crystal structure changes. Those microstructural changescan be harmful to the material properties, causing grain growth, reducedfatigue resistance and reduced ductility. Additionally, during brazingthe molten braze filler reacts with the parent metal, dissolving it anddiffusing into it, which can cause unwanted changes in the parent metaland brazed joint properties. The brazing temperature has to be kept aslow as possible and holding time has to be minimized as well to avoidthe aforementioned changes in the properties and structure of the partbeing brazed.

The addition of Zr to the Ti—Cu—Ni braze alloy allows melting (brazing)to occur at lower temperatures than does a Ti—Cu—Ni braze alloy withoutZr. The lowered brazing temperature results in reduced undesirablemicrostructure changes in the brazed parts after brazing. Reducedmicrostructure changes cause less embrittlement of the brazed parts.Because embrittlement is detrimental to the ductility and fatigueresistance of the brazed parts, the use of a Ti—Cu—Ni braze alloy withadded Zr, and the concomitant lowered brazing temperature, may result inbrazed materials with better mechanical properties than would otherwisebe obtained using a Ti—Cu—Ni braze alloy without added Zr.

U.S. Pat. No. 6,149,051 discloses a braze alloy of 40Ti-20Zr-20Cu-20Niin the form of a homogenous mixed powder braze filler. While useful forsmaller applications, powder braze fillers may present problems whenbrazing large sheet metal products. The filler must be uniformly coatedonto the parent metal sheets which require special equipment.

U.S. Pat. No. 6,475,637 discloses a Ti—Ni—Cu braze foil comprising10.5-12.5 wt % Zr which is formed by rapid solidification to produce ahomogeneous thin foil. The rapid solidified foil is limited in thewidth, length and quantity of the foil. Furthermore, the manufacture ofthe braze foil by rapid solidification can be relatively expensive.

As can be seen, there is a need for braze foils and sheets made of analloy of Ti, Zr and other metals that would have a low melting point andbe useful for brazing large sheet metal products. It would also bedesirable if such braze foils and sheets could be manufactured easilyand inexpensively.

SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided a braze sheetor foil comprising a core comprising at least one layer of titanium andat least one layer of zirconium; and at least one covering layercomprising commercially pure copper, a copper alloy, commercially purenickel, a nickel alloy or mixtures thereof, wherein the covering layerhas a metallurgical bond with said core.

In another aspect of the present invention there is provided a brazesheet or foil comprising a first metallic layer; a second metalliclayer; and a core comprising titanium and zirconium wherein the core isbetween the first and the second metallic layers.

In yet another aspect of the present invention there is provided a brazesheet or foil comprising a first metallic layer; a second metalliclayer; a third metallic layer; a fourth metallic layer; a fifth metalliclayer; a sixth metallic layer, and a core comprising titanium whereinthe first, second and third metallic layers are layered on one side ofthe core and the fourth, fifth, and sixth layers are layered on anotherside of the core and wherein at least one of the first, second, third,fourth, fifth or sixth layer comprises zirconium.

In a further aspect of the present invention there is provided a brazesheet or foil comprising a first metallic layer; a metallic secondlayer, the second layer metallurgically bonded to the first layer; athird metallic layer, the third layer metallurgically bonded to thesecond layer and wherein the third layer comprises zirconium; a corelayer, the core layer metallurgically bonded to the third layer andwherein the core layer comprises titanium; a fourth layer, the fourthlayer metallurgically bonded to the core layer and wherein the fourthlayer comprises zirconium; a fifth layer, the fifth layermetallurgically bonded to the fourth layer; and a sixth layer, the sixthlayer metallurgically bonded to the fifth layer.

In another aspect of the present invention there is provided a brazesheet or foil comprising a first layer, the first layer comprisingeither copper or nickel; a second layer, the second layermetallurgically bonded to the first layer and wherein the second layercomprises the other of either copper or nickel; a third layer, the thirdlayer metallurgically bonded to the second layer and wherein the thirdlayer comprises zirconium; a core layer, the core layer metallurgicallybonded to the third layer and wherein the core layer comprises titanium;a fourth layer, the fourth layer metallurgically bonded to the corelayer and wherein the fourth layer comprises zirconium; a fifth layer,the fifth layer metallurgically bonded to the fourth layer and whereinthe fifth layer comprises either copper or nickel; and a sixth layer,the sixth layer metallurgically bonded to the fifth layer and whereinthe sixth layer comprises the other of either copper or nickel.

In a yet another aspect of the present invention there is provided abraze sheet or foil comprising a first layer comprising nickel, copperor mixtures thereof; a second layer comprising titanium or zirconium; athird layer comprising nickel, copper or mixtures thereof; a core layercomprising titanium or zirconium; a fourth layer comprising nickel,copper or mixtures thereof; a fifth layer comprising titanium orzirconium; a sixth layer comprising nickel, copper or mixtures thereof;and wherein at least one of the layers comprises zirconium and at leastone of the layers comprises titanium.

In a further aspect of the present invention there is provided abraze-clad base material comprising a base material; and a braze sheetor foil metallurgically bonded to the base material, the braze sheet orfoil comprising a first layer comprising nickel, copper or mixturesthereof, a second layer comprising titanium or zirconium, a third layercomprising nickel, copper or mixtures thereof, a core layer comprisingtitanium or zirconium, a fourth layer comprising nickel, copper ormixtures thereof, a fifth layer comprising titanium or zirconium, asixth layer comprising nickel, copper or mixtures thereof and wherein atleast one of the layers comprises zirconium and at least one of thelayers comprises titanium.

In yet another aspect of the present invention there is provided amethod for brazing a base material comprising the steps of placing abraze sheet or foil between two base materials to be joined together,the braze sheet or foil comprising a first metallic layer, a secondmetallic layer and a core comprising titanium and zirconium wherein thecore is between the first and the second metallic layers; heating thebraze material and base materials to a brazing temperature; and forminga braze joint between the braze sheet or foil and the base materials.

In yet another aspect of the present invention there is provided amethod for brazing a base material comprising the steps of placing abraze sheet or foil between two base materials to be joined together,the braze sheet or foil comprising a first layer comprising nickel,copper or mixtures thereof, a second layer comprising titanium orzirconium, a third layer comprising nickel, copper or mixtures thereof,a core layer comprising titanium or zirconium, a fourth layer comprisingnickel, copper or mixtures thereof, a fifth layer comprising titanium orzirconium, a sixth layer comprising nickel, copper or mixtures thereofand wherein at least one of the layers comprises zirconium and at leastone of the layers comprises titanium; heating the braze material andbase materials to a brazing temperature; and forming a braze jointbetween the braze sheet or foil and the base materials.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a first example of a braze sheet orfoil according to the invention;

FIG. 2A is a block diagram showing a first example of the core layer ofthe braze sheet or foil of FIG. 1 according to the invention;

FIG. 2B is a block diagram showing a second example of the core layer ofthe braze sheet or foil of FIG. 1 according to the invention;

FIG. 3 is a block diagram showing a second example of a braze sheet orfoil according to the invention;

FIG. 4 is a block diagram showing a third example of a braze sheet orfoil according to the invention;

FIG. 5 shows the Differential Thermal Analysis (DTA) heating curve for aone-phase heating step of Ti20Zr20Cu20Ni, according to the invention;

FIG. 6 shows the DTA cooling curve for Ti20Zr20Cu20Ni heated in FIG. 5,according to the invention;

FIG. 7 shows the DTA heating curve for a two-phase heating step ofTi20Zr20Cu20Ni, according to the invention;

FIG. 8 shows the DTA cooling curve for Ti20Zr20Cu20Ni from FIG. 7,according to the invention; and

FIG. 9 is a flow chart showing a method of brazing a base material,according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Broadly, the present invention provides titanium braze sheets and/orfoils that may comprise layers of zirconium and titanium, structuralbase metal sheet with those braze sheets and/or foils clad to thesurface, as well as methods for using the braze sheets and/or foils forbrazing base materials. A “foil” is known in the art to be of athickness less than a sheet, and the common definition of “foil” is a“very thin sheet metal”. As used herein, a foil is taken to have athickness less than about 0.005 inches, and thus the term “sheet” isused to designate situations where the thickness is greater than about0.005 inches. In all other properties, i.e. composition and methods ofuse, the terms “foil” and “sheet” as well as “strip” are usedinterchangeably herein. In its most basic embodiment, the braze foilsmay comprise a core layer of titanium and zirconium and at least oneother layer that may cover the core layer. The other layer may comprisecommercially pure copper, a copper alloy, commercially pure nickel, anickel alloy or mixtures thereof. The core layer of zirconium andtitanium may comprise discrete layers of zirconium and titanium. Thebraze foils may also comprise more than these two layers. The number oflayers may be determined by the desired melting properties, the desiredthickness, and the application that the foil will be used in. The brazefoils of the present invention are suitable for applications wherever abraze foil with low melting point is required, such as, but not limitedto, aerospace industry.

Braze foils must have a lower melting temperature than the basematerials to which they are applied. Newer, lighter weight alloys suchas, but not limited to, titanium alloy require braze foils that may bebrazed at a low temperature while retaining good flow and coveragecharacteristics. The addition of zirconium to braze alloys, such asTi—Cu—Ni, lowers the melting point. Presently, braze alloys ofTi—Zr—Ni—Cu are either in a mixed, homogenous powder form or in ahomogenous foil, usually formed by rapid solidification of the meltedpowder form. The powder and homogenous foil forms of Ti—Zr—Ni—Cu brazealloys, while performing well in brazing applications, may be difficultto use and/or costly to manufacture. The braze foil of the presentinvention may comprise metallic layers of titanium, zirconium, nickeland/or copper that may be readily bonded together to form the braze foilwithout any intermediate heating. Brazing base materials with thelayered braze foils may result in a braze alloy of composition accordingto the weight-percentage of the individual sheets. Furthermore theresulting braze alloy may form a different metallurgical bond and/orcrystalline structure compared to the powder and homogenous foils of theprior art.

The addition of Zr to a Ti/Cu/Ni braze alloy may result in a lowermelting (brazing) temperature. Furthermore, the layering arrangement ofmetals in the braze foils can be ordered in such a way that the reactivecomponents, Ti and Zr, may not be exposed during the temperature rampingstate of the brazing process. For example, exposed, reactive Ti mayreact with the atmosphere during brazing to form, for example, Ti oxide,hydride or nitride when the atmosphere contains oxygen, hydrogen and/ornitrogen. The homogenous compositions of the braze foils known in theart require brazing in an inert atmosphere or in a vacuum to preventreaction of Ti with the atmosphere.

The braze foil of the present invention may comprise a plurality oflayers where the layers may be metallurgically bonded to each other. Theonly limitation on the number of layers may be the desired thickness andcomposition of the braze foil. In one exemplary embodiment, shown inFIG. 1, braze foil 10 may also comprise a core layer 16 comprising atleast one layer of zirconium and at least one layer of titanium as wellas a covering layer 12 where the covering layer 12 covers the core layer16 such that core layer 16 is not exposed to the atmosphere. Thecovering layer 12 may form a metallurgical bond with the core layer 16.In an illustrative embodiment, the covering layer 12 may comprisecommercially pure (CP) copper, a copper alloy, CP nickel, a nickelalloy, a copper/nickel alloy or mixtures thereof. The core layer 16 maycomprise, for example, one layer of zirconium and one layer of titanium.

Alternatively, as shown in FIG. 2A the core layer may comprise a firstlayer 22 of titanium between two second layers 20 of zirconium or afirst layer 22 of zirconium between two second layers 20 of titanium.The core layer 16 may further comprise at least two layers each oftitanium and zirconium where the zirconium and titanium layers arearranged in an alternating arrangement as illustrated in FIG. 2B.

In FIG. 2B, core layer 16 may comprise first layer 24 of eitherzirconium or titanium which alternates with a second layer 26 of theother of zirconium or titanium. It will be appreciated that although thefigures show layers of equal thickness for illustrative purposes, thelayers need not be of uniform thickness. Actual individual layerthickness will depend on the composition of the material in theindividual layer, the molecular weight or density of the elements in theindividual layer, the desired composition (weight %) of the finishedbraze foil, and the desired total thickness of the finished braze foil.In one embodiment, the layers may have individual thickness of fromabout 0.00005 inches to about 0.015 inches with a total braze foilthickness of from about 0.0005 inches to about 0.020 inches. In anotherillustrative embodiment, the layers may have individual thickness offrom about 0.0001 inches to about 0.0015 inches with a total braze foilthickness of from about 0.0010 inches to about 0.0020 inches. Exemplaryembodiments of the arrangement of layers in the braze foil may be, butnot limited to Cu/Ti/Zr/Cu, Cu/Ti/Zr/Ti/Cu, Cu/Zr/Ti/Zr/Cu,Cu/Zr/Ti/Zr/Ti/Cu, Ni/Ti/Zr/Ni, Ni/Ti/Zr/Ti/Ni, Ni/Zr/Ti/Zr/Ni,Ni/Zr/Ti/Zr/Ti/Ni, Cu/Ti/Zr/Ni, Cu/Zr/Ti/Zr/Ni, Cu/Ti/Zr/Ti/Ni,Cu/Zr/Ti/Zr/Ti/Ni or Ni—Cu/Zr/Ti/Zr/Ni—Cu where Ni—Cu represents anickel-copper alloy. It is contemplated that either the Cu or Ni layermay be replaced by a Cu/Ni alloy. In one illustrative embodiment, thecomposition of the braze foil may be, but not limited to, about 25 wt %Ti, about 50 wt % Cu and about 25 wt % Zr. In an alternate, non-limitingillustrative embodiment, the composition may be about 12.6 wt %zirconium, 15.4 wt % Ni and about 72 wt % Ti. In another non-limitingillustrative embodiment, the composition may be about 20 wt % zirconium,20 wt % Ni, 20 wt % Cu and about 40 wt % Ti. In a further illustrativeembodiment, the composition of the braze foil may comprise from about 10wt % to about 72 wt % Zr.

Braze foil 10 may further comprise a second covering layer to producebraze foil 30 shown in FIG. 3. Braze foil 30 comprises a core layer 36surrounded by a first covering layer 34 and a second covering layer 32.The core layer 36 may comprise at least one layer of zirconium and onelayer of titanium while the first covering layer 34 and the secondcovering layer 32 may comprise commercially pure (CP) copper, a copperalloy, CP nickel, a nickel alloy, a copper/nickel alloy or mixturesthereof. It is contemplated that first covering layer 34 and secondcovering layer 32 will have different compositions. By way ofnon-limiting example, the first covering layer 34 may comprise CP copperor a copper alloy while the second covering layer 32 may comprise CPnickel or a nickel alloy.

The braze foils of the present invention may further comprise additionallayers. The arrangement and/or composition of the layers may vary,resulting in a number of possible combinations of layers. By way ofnon-limiting example, braze foil 40 of FIG. 4 may comprise a first 42,second 44, third 46, fourth 50, fifth 52 and sixth 54 layers with a corelayer 48 between the first 42, second 44 and third 46 layers on one sideof core layer 48 and the fourth 50, fifth 52 and sixth 54 layers on theother side. For example, the first 42 and sixth 54 layers may be, butnot limited to CP copper, copper alloy, CP nickel, nickel alloy, acopper/nickel alloy or mixtures thereof. Additionally, the second 44,third 46, fourth 50 and fifth 52 layers may be, but not limited to, CPcopper, copper alloy, CP nickel, nickel alloy, a copper/nickel alloy,zirconium or titanium while the core layer may be zirconium or titanium.Braze foil 40 may comprise at least one layer of titanium and one layerof zirconium Exemplary embodiments of the arrangements of the layers maybe, but not limited to, Cu/Zr/Ni/Ti/Zr/Ni/Cu, Ni/Zr/Cu/Ti/Cu/Zr/Ni,Cu/Ni/Zr/Ti/Zr/Ni/Cu, Cu/Zr/Ni/Ti/Cu/Zr/Ni, Ni/Cu/Zr/Ti/Zr/Cu/Ni orCu/Ti/Ni/Ti/Zr/Cu/Ni. It will be appreciated that there are any numberof viable arrangements of the layers and, as the number of layersincreases, the number of permutations increases exponentially. Forexample, a braze foil with greater than seven layers may have the layersarranged as (Cu or Ni)/Zr/(Cu or Ni)/Zr/Ti/Zr/(Cu or Ni)/Ti/Zr/(Cu orNi).

In one illustrative embodiment, the braze foil may have a composition ofabout 40 wt % titanium, about 20 wt % copper, about 20 wt % nickel andabout 20 wt % zirconium. In an alternative illustrative embodiment, thecomposition of the braze foil may be about 37.5 wt % titanium, 15 wt %copper, 15 wt % nickel and 37.5 wt % zirconium. In a non-limitingembodiment, the braze foil may comprise from about 10 wt % to about 72wt % zirconium.

The layers of the braze foil may be clad to form the foils by cold orhot roll bonding. Roll bonding may typically be carried out in a bondingmill that provides sufficient pressure to form a metallurgical bond evenwithout heat treating (such as annealing, for example) between thedissimilar materials. In one embodiment, the cold rolling process ofU.S. Pat. No. 6,722,002, hereby incorporated by reference, may be usedto produce the braze foils of the present invention. The process mayinvolve taking an individual strip, or multiple strips, of Ti and Zrwith a strip, or multiple strips, comprised of CP Cu and/or Ni, alloysthereof, or combinations thereof, placed on both sides of the Ti or Zrstrip. The thus-placed strips may then be processed, such as beingcold-worked by processing with a rolling machine, for example, to thedesired thickness, resulting in a roll bonded, multi-layered alloystrip. Strips having 5, 6, 7, or more layers may be formed and thelayers may be arranged in any desired configuration such as, but notlimited to, the exemplary embodiments of the present invention. Thus, anindividual strip of the multi-layered alloy strip may be placed next to,and on both sides of, an individual strip, or multiple strips, of Ti andZr or some other layer or multi-layer strip. The thus-placed strips maythen be processed, such as being cold-worked by processing with arolling machine, for example, to the desired thickness, resulting in aroll bonded, multi-layered alloy sheet or foil useful for variousbrazing applications.

Other methods of forming the multi-layered braze sheets or foils with Zradded may also include starting with a core of Ti or Ti alloy, coatingthe core (using coating methods known in metallurgy practice) with atleast one or more layers of one or more of Cu, a Cu alloy, Ni, or a Nialloy. This multi-layer system may then be coated with at least one ormore layers of Zr, with or without intermediate cold-working steps.Further coating of the resulting multi-layer system with at least one ormore layers of one or more of Cu, a Cu alloy, Ni, or a Ni alloy, with orwithout intermediate cold-working steps may be performed. The resultingmulti-layered composite may then be cold-worked to the desired thicknessto a thin sheet or foil. It should be understood that the arrangement oflayers above is meant only as an illustration and that the method may beused to produce any desired arrangement of the layers.

Similarly, other methods of forming the multi-layered braze sheets orfoils with Zr added may also include starting with a core of Zr or Zralloy, coating the core using coating methods known in metallurgypractice with at least one or more layers of one or more of Cu, a Cualloy, Ni, or a Ni alloy. Then at least one or more layers of Ti, withor without intermediate cold-working steps may be layered on followed bycoating with at least one or more layers of one or more of Cu, a Cualloy, Ni, or a Ni alloy, with or without intermediate cold-workingsteps. The resulting multi-layered composite may then be cold-worked tothe desired thickness to a thin sheet or foil. It should be understoodthat the arrangement of layers above is meant only as an illustrationand that the method may be used to produce any desired arrangement ofthe layers.

The present invention also provides a braze-clad base material that maycomprise a base material with the braze foil of the present inventionbonded to the base material prior to brazing. The base material may be,but not limited to, titanium alloys, nickel alloys and stainless steel.The base material may be chosen to have a higher melting temperaturethan the braze foil. During the brazing process the braze foil may meltbut not the base material. Any of the braze foils contemplated by thepresent invention may be bonded to the base material by a metallurgicalbond prior to brazing such as during the production of the base materialand/or the braze foil. In one illustrative embodiment, the braze-cladbase material may have a layer of the base material between two layersof braze foil. In an alternative embodiment, the braze-clad basematerial may have a layer of braze foil on one side of the basematerial.

A method for using the braze foils of the present invention to brazebase materials is provided. Method 100, illustrated in FIG. 9, maycomprise step 102 of placing a braze sheet or foil between two basematerials to be joined together. The braze sheet or foil may comprise afirst metallic layer, a second metallic layer and a core comprisingtitanium and zirconium wherein the core is between the first and thesecond metallic layers. Method 10 may further comprise step 104 ofheating the braze material and base materials to a brazing temperature.The rate of temperature increase to reach the braze temperature may befrom about 1° C./min to about 10° C./min. Method 10 then may comprisestep 106 of forming a braze joint between the braze sheet or foil andthe base materials. After the braze joint is formed, the braze joint maybe cooled. Although not necessary, after the brazing temperature isreached, the temperature may be held for a desired amount of time beforecooling the braze joint to allow diffusion of the various elements intothe base material. Finally, the braze joint may be solidified.

It will be appreciated that the brazing temperature will be dependent onthe melting temperature of the braze foil which, in turn, is dependenton the composition of the braze foil. For example, if the braze foil hasa composition of about 40 wt % Ti, about 20 wt % Cu, about 20 wt % Niand about 20 wt % Zr, the melting temperature may be about 864° C.(1587° F.) (See, for example, FIG. 5). The brazing temperature may thenbe from about 840° C. to about 950° C.

Differential Thermal Analysis (DTA) is a technique that may be used tocharacterize the solidus and liquidus of roll bonded Ti—Zr—Ni—Cu alloyswherein the solidus is the temperature at which 100% of the alloy is ina solid crystalline form and liquidus the temperature at which it is ina fluid, non-crystalline form. The information may be useful todetermine the brazing temperature in brazing applications. Typicalheating and cooling DTA curves of 40Ti-20Zr-20Ni-20Cu (actual weight %of sample: 39Ti-21.6Zr-19.1Ni-19.6Cu-0.1 Fe) are shown in FIGS. 5-8.

FIGS. 5 and 6 show the heating and cooling curves, respectively, for a0.002 inch thick foil that was heated to 1050° C. at a rate of 1° C./minand subsequently cooled at a rate of 20° C./min. The liquidus andsolidus temperatures are identified from the cooling curve to be 864° C.and 843° C. respectively.

FIGS. 7 and 8 show the heating and cooling curves, respectively, for a0.0016 inch thick foil that was heated to 800° C. at a rate of 10°C./min, the temperature then held for 30 minutes, then raised to 950° C.at a rate of 5° C./min and finally cooled at a rate of 20° C./min. Theliquidus temperature is the same under these conditions as those ofFIGS. 5 and 6.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A braze sheet or foil comprising: a core comprising at least onelayer of titanium and at least one layer of zirconium; and at least onecovering layer comprising commercially pure copper, a copper alloy,commercially pure nickel, a nickel alloy or mixtures thereof, whereinthe covering layer has a metallurgical bond with said core.
 2. The brazesheet or foil of claim 1 wherein the core comprises a layer of titaniumcovered on each side by a layer of zirconium.
 3. The braze sheet or foilof claim 1 wherein the core comprises a a layer of zirconium covered oneach side by a layer of titanium.
 4. The braze sheet or foil of claim 1wherein the core comprises two layers of zirconium and two layers oftitanium, wherein the zirconium layers are alternating with the titaniumlayers.
 5. The braze sheet or foil of claim 1 wherein the covering layercomprises commercially pure copper or a copper alloy.
 6. The braze sheetor foil of claim 5 wherein the braze sheet or foil has a composition ofabout 25 wt % titanium, about 50 wt % copper and about 25 wt %zirconium.
 7. The braze sheet or foil of claim 1 wherein the coveringlayer comprises commercially pure nickel or a nickel alloy.
 8. The brazesheet or foil of claim 7 wherein the braze sheet or foil has acomposition of about 12.6 wt % titanium, about 15.4 wt % nickel andabout 72 wt % zirconium.
 9. The braze sheet or foil of claim 1 whereinthe covering layer comprises a nickel-copper alloy.
 10. The braze sheetor foil of claim 9 where in the braze sheet or foil has a composition ofabout 40 wt % titanium, about 20 wt % zirconium, about 20 wt % nickeland about 20 wt % copper.
 11. The braze sheet or foil of claim 1 whereinthe zirconium has a weight percentage of from about 10 wt % to about 72wt %.
 12. The braze sheet or foil of claim 1 wherein the core has ametallurgical bond with the covering layer, the metallurgical bondformed by roll bonding the core with the covering layer withoutintermediate heat treating.
 13. The braze sheet or foil of claim 1further comprising at least one second covering layer comprisingcommercially pure copper, a copper alloy; commercially pure nickel, anickel alloy or mixtures thereof, wherein the second covering layersubstantially covers the at least one covering layer.
 14. The brazesheet or foil of claim 13 wherein the covering layer has a metallurgicalbond with the second covering layer wherein the metallurgical bond isformed by roll bonding without intermediate heat treating.
 15. A brazesheet or foil comprising: a first metallic layer; a second metalliclayer; and a core comprising titanium and zirconium wherein the core isbetween the first and the second metallic layers.
 16. The braze sheet orfoil of claim 15 wherein the core has a metallurgical bond with thefirst and the second metallic layers wherein the metallurgical bond isformed by roll bonding the core with the first and second metalliclayers without intermediate heat treating.
 17. The braze sheet or foilof claim 15 wherein the first and second metallic layers comprisecommercially pure copper, a copper alloy, commercially pure nickel, anickel alloy or mixtures thereof.
 18. The braze sheet or foil of claim17 wherein the first metallic layer comprises commercially pure copperor a copper alloy and the second metallic layer comprises commerciallypure nickel or a nickel alloy.
 19. The braze sheet or foil of claim 17wherein the first and second metallic layers comprise commercially purecopper.
 20. The braze sheet or foil of claim 17 wherein the first andsecond metallic layers comprise commercially pure nickel.
 21. The brazesheet or foil of claim 15 wherein the first and second layers comprise anickel-copper alloy.
 22. The braze sheet or foil of claim 21 wherein thecore layer comprises one layer of titanium between two layers ofzirconium.
 23. A braze-clad base material comprising the braze sheet orfoil of claim 15, wherein the braze sheet or foil is bonded to one orboth sides of a base material by a metallurgical bond.
 24. The brazesheet or foil of claim 15 wherein the core comprises at least one layerof zirconium and at least one layer of titanium.
 25. A braze sheet orfoil comprising: a first metallic layer; a second metallic layer; athird metallic layer; a fourth metallic layer; a fifth metallic layer; asixth metallic layer, and a core comprising titanium, wherein the first,second and third metallic layers are layered on one side of the core andthe fourth, fifth, and sixth metallic layers are layered on another sideof the core and wherein at least one of the first, second, third,fourth, fifth or sixth layer comprises zirconium.
 26. The braze sheet orfoil of claim 25, wherein at least one of the metallic layers comprisescommercially pure copper.
 27. The braze sheet or foil of claim 25,wherein one or more of the first metallic layer, the second metalliclayer, and the third metallic layer comprises one or more of zirconium,copper, or nickel, and further wherein one or more of the fourthmetallic layer, the fifth metallic layer, and the sixth metallic layercomprises one or more of zirconium, copper, or nickel.
 28. The brazesheet or foil of claim 27, wherein the second metallic layer compriseszirconium and is sandwiched between the first metallic layer and thethird metallic layer.
 29. The braze sheet or foil of claim 28, whereinthe second metallic layer has a metallurgical bond with both the firstand the third metallic layers, the metallurgical bond formed by rollbonding the first, second, and third metallic layers together withoutheat treating.
 30. The braze sheet or foil of claim 27 wherein the thirdand fourth metallic layers comprise zirconium, wherein the thirdmetallic layer is sandwiched between the second metallic layer and thecore layer and the fourth metallic layer is sandwiched between the fifthmetallic layer and the core layer.
 31. The braze sheet or foil of claim25, wherein the second and fifth metallic layers comprise zirconium, andwherein the first metallic layer comprises one of copper or nickel andthe third metallic layer comprises the other of copper or nickel, andfurther wherein the fourth metallic layer includes one of copper ornickel and the sixth metallic layer includes the other of copper ornickel.
 32. The braze sheet or foil of claim 31, wherein the core has ametallurgical bond with the third and the fourth metallic layers formedby roll bonding without intermediate heat treating.
 33. The braze sheetor foil of claim 32, wherein the second metallic layer has ametallurgical bond with the first and third metallic layers and whereinthe fifth metallic layer has a metallurgical bond with the fourth andsixth metallic layers, and further wherein the metallurgical bonds areformed by roll bonding without intermediate heat treating.
 34. A brazesheet or foil comprising: a first metallic layer; a second metalliclayer, the second layer bonded to the first layer by a metallurgicalbond; a third metallic layer, the third layer bonded to the second layerby a metallurgical bond and wherein the third layer comprises zirconium;a core layer, the core layer bonded to the third layer by ametallurgical bond and wherein the core layer comprises titanium; afourth metallic layer, the fourth layer bonded to the core layer by ametallurgical bond and wherein the fourth layer comprises zirconium; afifth metallic layer, the fifth layer bonded to the fourth layer by ametallurgical bond; and a sixth metallic layer, the sixth layer bondedto the fifth layer by a metallurgical bond.
 35. The braze sheet or foilof claim 34 wherein the first and sixth layers comprise commerciallypure copper or a copper alloy and the second and fifth layers comprisecommercially pure nickel or a nickel alloy.
 36. The braze sheet or foilof claim 34 wherein the first and sixth layers comprise commerciallypure nickel or a nickel alloy and the second and fifth layers comprisescommercially pure copper or a copper alloy.
 37. The braze sheet or foilof claim 34 wherein the zirconium has weight percentage of from about 10wt % to about 72 wt %.
 38. A braze sheet or foil comprising: a firstlayer, the first layer comprising either copper or nickel; a secondlayer, the second layer bonded to the first layer by a metallurgicalbond and wherein the second layer comprises the other of either copperor nickel; a third layer, the third layer bonded to the second layer bya metallurgical bond and wherein the third layer comprises zirconium; acore layer, the core layer bonded to the third layer by a metallurgicalbond and wherein the core layer comprises titanium; a fourth layer, thefourth layer bonded to the core layer by a metallurgical bond andwherein the fourth layer comprises zirconium; a fifth layer, the fifthlayer bonded to the fourth layer by a metallurgical bond and wherein thefifth layer comprises either copper or nickel; and a sixth layer, thesixth layer bonded to the fifth layer by a metallurgical bond andwherein the sixth layer comprises the other of either copper or nickel.39. The braze sheet or foil of claim 38 wherein the braze sheet or foilhas a composition of about 40 wt % titanium, about 20 wt % zirconium,about 20 wt % copper and about 20 wt % nickel.
 40. The braze sheet orfoil of claim 38 wherein the braze sheet or foil has a composition ofabout 37.5 wt % titanium, about 15 wt % copper, about 15 wt % nickel andabout 37.5 wt % zirconium.
 41. The braze sheet or foil of claim 38wherein the braze sheet or foil has a thickness of from about 0.0005inches to about 0.020 inches.
 42. The braze sheet or foil of claim 38wherein the braze sheet or foil has a thickness of from about 0.0010inches to about 0.0020 inches.
 43. A braze sheet or foil comprising: afirst layer comprising nickel, copper or mixtures thereof; a secondlayer comprising titanium or zirconium; a third layer comprising nickel,copper or mixtures thereof; a core layer comprising titanium orzirconium; a fourth layer comprising nickel, copper or mixtures thereof;a fifth layer comprising titanium or zirconium; a sixth layer comprisingnickel, copper or mixtures thereof; and wherein at least one of thelayers comprises zirconium and at least one of the layers comprisestitanium.
 44. The braze sheet or foil of claim 43 wherein each of thelayers has a metallurgical bond with any adjacent layer, themetallurgical bond formed by roll bonding without intermediate heattreating.
 45. The braze sheet of foil of claim 43 wherein the first andsixth layers comprise commercially pure nickel, the second and fifthlayers comprise zirconium, the third and fourth layers comprisecommercially pure copper and the core layer comprises titanium.
 46. Thebraze sheet or foil of claim 43 wherein the braze sheet or foil has acomposition of about 40 wt % titanium, about 20 wt % zirconium, about 20wt % copper and about 20 wt % nickel.
 47. The braze sheet of foil ofclaim 43 wherein the first and sixth layers comprise commercially purenickel, the second and fifth layers comprise commercially pure copper,the third and fourth layers comprise zirconium and the core layercomprises titanium
 48. The braze sheet or foil of claim 43 wherein thebraze sheet or foil has a composition of about 37.5 wt % titanium, about15 wt % copper, about 15 wt % nickel and about 37.5 wt % zirconium. 49.A braze-clad base material comprising: a base material; and a brazesheet or foil bonded to the base material by a metallurgical bond, thebraze sheet or foil comprising a first layer comprising nickel, copperor mixtures thereof, a second layer comprising titanium or zirconium, athird layer comprising nickel, copper or mixtures thereof, a core layercomprising titanium or zirconium, a fourth layer comprising nickel,copper or mixtures thereof, a fifth layer comprising titanium orzirconium, a sixth layer comprising nickel, copper or mixtures thereofand wherein at least one of the layers comprises zirconium and at leastone of the layers comprises titanium.
 50. The braze-clad braze materialof claim 49 wherein the first and sixth layers comprise commerciallypure nickel, the second and fifth layers comprise zirconium, the thirdand fourth layers comprise commercially pure copper and the core layercomprises titanium.
 51. The braze-clad braze material of claim 49wherein the base material comprises a titanium based alloy, a nickelbased alloy or stainless steel.
 52. A method for brazing a base materialcomprising the steps of: placing a braze sheet or foil between two basematerials to be joined together, the braze sheet or foil comprising afirst metallic layer, a second metallic layer and a core comprisingtitanium and zirconium wherein the core is between the first and thesecond metallic layers; heating the braze material and base materials toa brazing temperature; and forming a braze joint between the braze sheetor foil and the base materials.
 53. The method of claim 52 furthercomprising the step of cooling the braze joint.
 54. The method of claim52 further comprising the step of solidifying the braze joint.
 55. Amethod for brazing a base material comprising the steps of: placing abraze sheet or foil between two base materials to be joined together,the braze sheet or foil comprising a first layer comprising nickel,copper or mixtures thereof, a second layer comprising titanium orzirconium, a third layer comprising nickel, copper or mixtures thereof,a core layer comprising titanium or zirconium, a fourth layer comprisingnickel, copper or mixtures thereof, a fifth layer comprising titanium orzirconium, a sixth layer comprising nickel, copper or mixtures thereofand wherein at least one of the layers comprises zirconium and at leastone of the layers comprises titanium; heating the braze material andbase materials to a brazing temperature; and forming a braze jointbetween the braze sheet or foil and the base materials.
 56. The methodof claim 55 further comprising the steps of: cooling the braze joint;and solidifying the braze joint.
 57. The method of claim 55 wherein thebraze sheet or foil has a composition of about 40 wt % titanium, about20 wt % zirconium, about 20 wt % copper and about 20 wt % nickel. 58.The method of claim 57 wherein the brazing temperature is from about840° C. to about 950° C.
 59. The method of claim 58 wherein the brazefoil or sheet and the base materials are heated to the brazingtemperature at a rate of about 1° C./min to about 10° C./min.